Rate of polyethylene wear correlates with earlier glenoid implant failure in anatomic total shoulder arthroplasty with cemented all-polyethylene glenoid components

Background

Glenoid component loosening is the most common cause of anatomic total shoulder arthroplasty failure, and osteolysis is a common intraoperative and radiographic finding associated with these failed arthroplasties. While preclinical testing can estimate failure mode and wear rates in the laboratory, there is limited in vivo data measuring polyethylene wear rate and location.

Methods

Using an institutional review board–approved total joint arthroplasty retrieval collection, 56 cemented all-polyethylene glenoid components from eleven different manufacturers were analyzed for in vivo dimensional change. We used the differential thickness measurement between the anteroposterior and superoinferior axes of each radially symmetrical implant to determine the dimensional change along that axis. A physiologic wear vector was determined for each retrieved device.

Results

The implants had a median dimensional change of 0.13 mm/year (range 0.01-1.01mm/year) and the 25^th and 75^th percentiles were 0.060 and 0.22 mm/year, respectively. The average time to revision of devices with <0.1mm/year of wear was 140.9 months, while the averages for devices between 0.1-0.2mm/year and ≥0.2mm/year were 80.7 and 54.0 months, respectively. Devices with ≥0.2mm/year of wear had significantly shorter time to revision than those with <0.1mm/year (P = .0006). The devices had a similar material loss distribution in both superior-inferior and anterior-posterior directions, with 29 (52%) devices having a greater material loss in the superior-inferior distribution and the remaining 27 (48%) devices in the anterior-posterior axis. The physiologic wear vector had a mean of 47.3 degrees, with a relatively even distribution across all angles, suggesting that glenoid component loosening can occur along multiple axes.

Conclusion

We conclude that polyethylene wear is a contributing factor for early failure of cemented all-polyethylene glenoid implants and that anatomic total shoulder arthroplasty may benefit from advances in polyethylene processing. We also suggest that in vitro testing of new polymers and designs should incorporate motion vectors beyond the traditional IS rocking horse test.